Apparatus for curing pneumatic tires



Filed Nov. 15. 1945 5 sheets-Sheet 1 T.l A. TE GROTENHUIS APPARATUS FOR CURING PNEUMATIC TIRES Filed Nov. l5, 1945 Y ct. 19, 1948.. v

5 Sheets-Sheet 2 .w s u v Mm 0 El WF@ la A u 1, A n JM o e h T Oct.' 19, i948. l r. A. TE GRoTENHUls 2,451,992

APPARATUS FOR CURING PNEUMATIC TIRES i Filed NOV. 15, 1945 l INVENTOR. Theodor@ A. Te Grotenhuis ATTO 5 Sheets-Sheet 3 @et 19, 1948. T, A, TE GROTENHUls 2,451,992

APPARATUS FOR CURING PNEUMATIC TIRES Filed Nov. 15, 1945 5 Sheets-Sheet 4 INVENTR. Theodqre A. Te rotenhuis ATTOR E'Ys Oct. 19, 1948.

Filed Nov. 15. 1945 T. A. TE GROTENHUIS APPARATUS FOR'CURING PNEUMATIC TIRES 5 Sheets-Sheet 5 Theodore Te rotenhuis ATTOR l This application is a division terials has taken place. quencytocause heating of ,rubber is advan- Patentecl Oct. 19, 1948 AllIAlitAVl?USy FOR CURING PNEUMATIC TIRES Theodore A. 'Ee Grotenh assigner -to The Gene uis, lmsted. Falls, Ohio, ral Tire & Rubber Com pany, Akron, IOhio, a corporation of Ohio lOriginal v application 531,920. f Divided and bei' 15, 1945, Serial January 3 1, 1945 5 Claims.

of my `,copending application Serial No. 531,920led April 20, 1944,

which has become Patent No', 2,438,952, and 'the .invention relates to an apparatus for making pneumatic tires. .e l' That. high voltage and high frequency oscillations, rapidly heat dielectrics,,includingrubben wood, glass, plastics and .other non-conductors,

has long been known to manufacturers of electricalcondensers, cable and the like, and in the design of condensers, cable and other apparatus adapted to operate under relativelyihigh frequency conditions provisionis always made to decrease the stress in the dielectric so that such i heatdeveloped is dissipated by. conduction and is notbuilt up to destructive values.

It has heretofore been proposed to utilize heat thus generated to cause curing of rubber, polymerization and/or setting of thermoplastic or thermosetting resinsand since the designing and building of. high frequency generators of .substan- April 2i), 1944, Serial No.

this application Novem- No. 628,731. in Canada Cl. lli-38) tial .capacityhas made such heat less expensive,

relatively wide commercial use of vhigh frequency and highvoltage equipment to form heat through relatively/'thick or relatively non-conductive ma- .The use of high fretageous over the pplication of heat externally becausel the .heat may be formed Lsubstantially uniformly throughout thearticle, i. e. the heat ,generated in thecenterof anarticle'subjected -to `uniform electric iield is justas great as the .heatgenerated at the yedgeswhereas.when heat k1s applied from the outside of relatively thick,

non-conductive materials, such as solid dielectrics,

u, a relatively long interval of time elapses before the temperature of thecenter of the article be- .comes equal to theternperature at the sideedges thereof.

. Even thoughthe advantages of high 4frequency iisuallypccurs, The presence. of metallic beads, thehun-uniform thickness .ofthe article, and the .requirement of stretchable. airbagshas hereto- Aforet preventedy the. application of. high frequency i ..currentin the, mold."

, ,.Bfecause of thelrelatively slow .penetration of heat'. )fromV external. Isurfaces intotliejrubber, relativelysl w acceleratorsgwith Arelativel Eilat curing `.1.Lagregara.cesser.. ...gemelli exclusively, as otherwise extreme variation in degree .of cure in different parts of the tire casing occurred.

It is another object to provide `a system for curing pneumatic tires wherein high frequency electrical energy is utilized to form heat within the rubberlike material.

It is another object, of the present invention Vto provide `a method yfor Vcuring pneumatic tires fluid pressure.

It is still another object to providerJ tire curing air bag which is iieXib-le and stretchable in all required directions, which Icontains means for effecting electricall connection tol a high frequency generator, and which c iperatesv toldistribute electrical potential so as to give a eld through the desired portions of a tire when thelatter is incorporated in the `mold land thel high.A frequency electric field is applied between the mold and the desired portions of the air bag.

It is another `object to provide apparatus for molding tirev casingsv under V heat and pressure wherein a high frequency electrioield may be used to generate heatinsitu Within the, interior thereof and rapidly acting acceleratorskrnay be used and the time required for curingmay be substantially reduced.

Other objects will be apparent from the following detailed description of the invention as illustrated by the accompanying drawings, where like parts are designated by like numerals of reference throughout the severalviews, in which:

Fig. 1 is an elevational View, partly in `section,A

of apparatus embodying thepresentinvention jected to my curing process;

Fig. 2 is a plan view, withvparts broken away, of the apparatus showninFig. 1; Fig. 3 is a plan View of an air bag embodying the present invention, showing schematically electrical connectionsto generator and to a portion ofaAtire-forming mold.

Fig. 4 is a sectional viewon the line. 4-4 of Fig. showing in dottedlines theoutline fof; a tire casing;

Fig, 5 is a sectionalvievv through ainodied form of apparatus Yer'nbody'ing,th e prese`ritinver1 ra suitable high frequency a modied form of air bag in a tire within a modified form tion with casing which is disposed of tire forming mold;

Fig. Gis a fragmentary View of an air bag, with parte broken away to show means for making electrical connection;

Fig. 7 is an elevational view of a portion of a modified form of air bag, with parts broken away to show stretchable metallic electrical conductors;

Fig. 8 is a sectional View Fig. '1;

Fig. 9 is an enlarged perspective view of a portion of a meshwork of stretchable conductors that may be used;

Fig. 10 is a sectional view through a mold embodying the present invention, showing means for making connection to induction bead heaters which may be used to supply heat to the substantial mass of metal within the beads of the tire casing;

Fig. 11 is a schematic view showing the connection of the induction bead heating elements in the apparatus of Fig. 9 to a suitable source of low frequency alternating current supply;

Fig. l2 is an enlarged View of a portion of the tire bead showing a splice which may be present to join the ends of the wire together so as to make a complete circuit and thus facilitate induction heating;

Fig. 13 is a sectional view through the preferred form of apparatus embodying the present invention showing a modified form of mold having disposed therein a tire casing containing a modified form of air bag;

Fig. 14 is an elevational view with a part broken away of a portion of the preferred form of air bag shown in Fig. 13 showing one way of attaching conductive leads to the separately insulated annular stretchable electrical. conducting surface portions thereof;

Fig. 15 is a sectional view, taken on l-l5 of Fig. 14; and 1 I Fig. 16 is a schematic view showing thear rangement of the conductive elements of the air bag with relation to the conductive surfaces of the mold and diagrammatically showing suitable connections for selectively connecting the conduo. tive surfaces to the high frequency generator to on the line 8-8 of the line provide the desired amount of energy for dier- Y ent portions of the tire.

In accordance with the present invention, the portions of the tire having variable thicknesses rare treated with differing amounts of high frequency electrical energy per unit of surface to form the desired amount of internal heat for curing of the vulcanizable rubber or rubbery composition of the tire. It is found that especially desirable results are had when use is made of relatively highly conductive soft rubber compositions to more evenly distribute the high frequency elec tric eld to the desired portions of the tire casing and to increase the uniformity of heat throughout the tire. Internal heat, provided by rapid change of electrical stress in the dielectric, is preikerably supplemented by external heat supplied to at least one or both of the surfaces with which the tire is brought in contact.

In accordance with the present invention, the dissipation of different amounts per unit .of surface area of high frequency electrical energy as heat in separate vportions of the tire casing (having stress resisting elements such as cords, fabrics, etc., to be adhered through one or more vulcanizable elastomers or rubbery polymers or condensation products including those rubbery materials hereinafter set forth) may be had by varying the spacing between the conductive surfaces of the mold or of the air bag from portions of the inner and outer surfaces of the tire casing, or by providing a plurality of separately insulated, annular conductive elements or surfaces on either one or both sides of the tire casing. Thus, if a single conductive layer is utilized in the air bag, portions thereof may be spaced at greater distances from the thinner portions of the side walls of the tire than from the inner surfaces of the tire adjacent the shoulder portions, or portions of the conductive surface of the mold may be spaced at varying distances from the face of the nearest surface of the tire casing so as to provide a more uniform eld and hence uniform heating throughout.

When separately insulated annular conductive surface portions are utilized on one or both sides of the tire, a high frequency electrical energy, either of the same or different potentials, is applied between selected, oppositely disposed surfaces to cause the dissipation of increased quantities of energy (per unit of surface area parallel to the outer surface of the air bag) in the thicker portions of the tire, so that the same heat per unit of volume of composition may be formed in situ if desired.

Referring more particularly to the drawings, wherein like parts are designated by like numerals of reference throughout the several views, it will be seen that a tire casing l, of any desired size, containing any suitable vulcanizable rubber-like composition such as natural or syntheticrubber vuicaniaable with sulfur or by appropriate treatment and having a suitable air bag 2 disposed therein, is cured while disposed within a suitable forming mold 3. The curing is accomplished by the aid of high frequency energy supplied from a suitable source, such as a high frequency generator 5 between conductive layers or areas disposed on opposite sides of the tire casing.

The mold may be of metal which is longitudinally split to provide upper and lower halves 3a and 3b, which may cooperatively form a single rigid conductive surface to contact the outside of the tire casing. The mold halves 3a and 3b are preferably disposed in contact with suitable heating means, such as steam `or other hot fluid, which may be supplied to cavities 6a and Bb formed by the respective halves 3a and 3b and respective upper and lower walls la and 1b of the watch case type heater 4, which serves a means for mounting or carrying the mold halves. The mold halves may be provided with conventional closing and opening mechanisms and are pivoted about the bolt B to permit separation thereof for extraction or insertion of the tire casing.

In accordance with one phase of the present invention, wherein heat is supplied to the beadforming areas by the production of induced current therein, it is desirable to prevent metal-tometal contact between the mold halves and the walls 1a, and '1b. For this reason gaskets H and i2 may be provided between the mold halves and the metal members to which they are attached. Gaskets I3 may be provided between attaching bolts I4 and the mounting means to which the mold members are attached.

The air or fluid pressure bag 2 having means such as a tubular conduit 5U for supplying fluid pressure to the cavity thereof from the pipe 5I,

separately insulated source of steam or water onerosa pressure. or the like (not. shown), comprises `the combination. of;` a stretchable conductive surface and avrelatively non-conductive mbber-like materiali;y The stretchable conductorsy or` conductive surface:` 'preferably` used may :comprise af. layercr area of relatively highly conductive,.soft rubber composition, in. combination with .1a4 contacting metal .conductor/ which .may serve: .as means. for making aelectrical connection -with :a substantial area `of the conductive rubber. composition,l The vconductive-rubber composition. serves to. distrib- -ute .the high orA radio.frequency-electric" eld through the, desired portion yof .the dielectricl be.- ing cured.

The conductive, soft, vulcanized `rubberlike compositions utilized inthe present. inventionas potential distributors preferably have a'resistance of 100 ohms/cm. ycubeoraless; however, conductive, soft, rubber compositions having .a resistance as. high as 5,000 or 10,000 ohms/cmcube or even more may be used, particularlyV inconjunction with relatively closely. spaced.` metallic conductors or when the current used is 110W.. `Rub,- ber compositions having aresistance greater than a megohms/cm. cubeare not suitable for most applications unless used in conjunction with auxiliary metallic conductors as hereinafter described. y i

Itis found that conductive rubberlike compositions; prepared by mixing `with a rubberlike mate,- rial the usual desired compounding ingredients and a substantial amount, say 20 to 50or60 parts per 100- parts of rubberlikematerial, of a carbon black-having a structure such as that deposited fromacetylene, :areparticularly effective for distribution of electricalA potential. Such'ia black maybe obtained commercially from Shawinigan Chemicals Limited.v

The method of preparing the conductive rubberlike material is exceptionally important if vthe greatest conductivityis to be had. The black and .other compounding agents are preferably'prepared as aqueous dispersions and mixed with an aqueous dispersion Yof the rubberlike material, such for example as naturallatex, in the desired proportions, -The rubber stock is preferably formed to the desired shape by any of the `known procedures for preparing latex articles directly fromthe compounded latex AWith-out mastication. When the amount of mastication is reduced to a minimum, the proportion of the black remaining as-an external, interconnected, conductive phase appears to-be greater than When substantial masticaticnofthe. mix is had. It is thought that itis for this reason that higher conductivity of compositions deposited directly from the oompoundedlatex is had. When the amount of carbon black dispersed'in the latex is so `large that an adherent lm is'not readily produced by drying thelatex (With orwithout a gellingagent and pregelling) .directly inthe desired form, or 'if latex casting procedures. are not desired, the entirely oronly partially dried coagulumvfrom the compounded latex may vbe extruded through relatively ne orifices or passageways in accordance with injection molding procedures to producea composition inthe lforni of sheets or strips,v or

-other shapes as desired, for use in molding the conductive rubber article of the present` invention. The composition may also bey formed 'in y 5 accordance with conventional rubberlike proeesses utilizing a minimum of mastication. i Other highly. conductive, strevtchable ,compositions such las those `obtained ley-mixing large amountsrof graphite into a;-y.ulcanizable rubberlikecomposition. may also.- be `usedto. .obtain/sementitheedvantages.:v

The rubberlike materials ofthe `conductive compositions-:includeanatural. rubber, 4polymers of one or more of butadiene;ihomologuesrorcana.- v logues .thereof ',rbuna;A lrubbers. (copolymera hav-ing at.` least .f5.0 .partsszoi onel orwmorefcconjugated dienes, :such las butadiene: and. isoprene, andi with one or .more other:` i copolymerizable.:.unsaturated -materials :such .forfexamplexas styrene, vinyl,- chlo- \ride, :h1or-subs-titutedc` styrenes, -..methyl J methacrylates, acrylonitrilep. dimethylv:.vinylethynylcarbinol, vinyl pyridine,I vinyliden'echloride',vand others), fneoprenefipolysulde condensartionprcd.- -ucts withu.auadiesubstituted organice. componi-nd Vsuchmir:exampleasfoleiin pclysuiidesc?A including -bothfthe. curable.;.1and. non-curable typed.; which are,l availablef :under the trade'...namela-Thiokol;:las

. welll as .butylg-.rubbers ;1 (copolymerizationi products provided with an. out'erzlayerr .I Bsof frubberlikefm'aterial having:varying` ..thicknesssz The thickness of the .rubberlike i material-: I 81 preferably' varies inversely. asisthe thickness :.ofothef tire .cross-.sec-

tionnearestvthereto,.sozthat theish'ort'est-1distance yfrom each portionofthe'outer surface ofL the .conductive layer I6 :.td'the .nearesttportiona ofwthe :inner surface'v offthe conductive rsurfacel 0. of the Vforming moldris about constant.. Thus, since-,the side .Wall portionstaof -:pneumatic: tires generally have-a'relatively` thin cross.A sectional thickness, the thicknesssof the relatively#non-conductive :soft-rubberlikematerial 'i8` ofi the air 'bag adjacent the tire side Wall is preferably greatest.:..n `the other 1 handuzfadj acent. they shoulder .portions .fofi the; tire the vstretchable iresilient conductorsare preferably'mcontact Wththesurfacexi Byselectingwa dielectricamaterial of relatively -lower powergfactorf 4than has. the. composition Vofl the: .tire being'. cured, some: `selectivity 1in'. 4:the

yheatirigof the i. tire .may ber-provided. .Ifthei ma- ?terial zlsghasa" lower dielectric,- constant',` the P,thickfnessof-athe thickerportionsr thereof `isa .preferably increased to.:obtainz\ a iuniform: iield...f Sincethe eld .pbetweeni ,.various.: poi-nts: ,.of; the .conductive :layer Jvgand therportionsof` the surfacezrznfnearest thereto varies inversel/yfasithe squarey ofthe.' dista nce.and .only inversely Las .theirst powertofzthe .dielectric constant, .-it' is seen thatiifenriency.` for :an increasedyeldzby ilse of thecompcsitiorryli? Vhaving: az `lower;idielectri-c. constantfmay, be :read-ily offset,` by,V a .slight increase-.in @thicknessthereofx Connectingfmeansisuch asametalllead Zwvhich may be connectedeto fa termina-1: `25:1 ofzthe high :frequency generator: wbyza :connecting wire-2.6 is provided.for..malcingz :electrical-connectiomghe- Ytween .fthe stretchablei resilient; f conductive '.:layfer i I6 and a. high frequency.'source. TVThe metalflead .23 is .tpreferably-1disposc-d; Withirn` suitablezinsula'- tion 21, e. g. tubular insulatorssoff porcelain, an evacuated, co;axia,l chamber; rubber-pr. other-lma- `terial ftpreyenie the .making-fof;:metalz-toemetal .f contact between :its and the; moldixomsurfacesrnf ene-1,992

to the rigid conductive surface such asthe surface 200i` the mold disposed over the outside portionsof the tire casing l. f

-Annular insulators, such as the rings 22fyvhich are` held within the inner peripheral portions of the mold halves 3a and 3b, are preferably provided to bear against the .inner periphery ofrthe air bag and to prevent shorting ofthe iield..f Inductive heating means, such as ycoils disposed within theannular insulators 2.2 andconnected in series relation :as ,illustrated in1Fig.'11 to a `suitable transformer 36, or other suitable source ofk alternating current of relativelylow or commercial frequency,'..are preferably vprovided for supplying heat to the mass ofmetal withinbeads 31 Vof the tire casing;` The coils; 35 are connected to provide superimposed magnetic elds having `lines `of force following themold and entirely circumventing the cross section of the beads. The

ends of the individual wires of the'beads 31 are preferably connectedtogether by suitable means, such as a splice 38 (Fig. 12), to provide. a closed electrical circuit, Yor one or moreclosed loops of wire may belincorporated, in` the` beads to serve as inductive heatinglmeans therefor.' l

vTo prevent substantial induced currentin the moldv halves 3a and 3b, transverse. insulating -1,000,000 to 10,000,000 for more cycles per second and having a suitable potential preferably of severa-l` thousand volts, `or suflicient to produce the requiredamountv of straininthe dielectric'ma- ,.terial, is supplied from the suitable generator.. 5 lbetween the stretchable conductors, such as the layer i6 and the conductive Asurface 20 of the mold, heat is producedin situ throughout the rubberlike material therebetween. Lower than 1000 volts may be used however. l

Since-the outer conductive surface'of the layer I6 is -closer to the inner surface' :Il of the tire cas- -ing in the `region of the shoulder thereof, the

energy per unit of surfacearea` 'dissipated vinternally of the shoulder region of thetire is Egreater and .the heatformedin situperunit volume of rubberlik'e material may be substantially the same 'as that in thinner portions ofthe tire. The heat supplied externally of the tire l'carcass from the steam or heating iiuid within thecavity 6a Vis found lto be desirable-infsmoothingout some of the variations duev tor anyvariation inintensity of the electric leld. Y

In thefrnodicationshown in Fig; `5`, the' electricallyl conductive surface t0 of the rigid formzing moldfhalvesfSc' and 3d is displaced at fvarying distances from the outer surface 55 of the' tire casing by non-conductive rigid material 56, sil-ch for example as porcelain, Pyrex glass, fused quartz, etc., the thickness-of vthe non-conductive material 56. being greater where the thickness of the tire'section is less.

The air bag 2a, may be entirely of conductive rubber composition, with or without auxiliary metal conductors disposed therein, or it may have a stretchable conductive surface layer ISa with means for making electrical connection thereto .carried by the non-conductive rubberlike composition 18a, the stretchable conductive material 56a preferably being an outer layer.

' To provide selective heating of the tire casing,

the rigid insulating material 5G may be selected so as tohavea lower power factor than the composition of the tire. Each portion of the outer surface -of the stretchable conductive layer is disposed with relation to the nearest portion of the rigid conductive surface 2D, so that a field of desired uniformity may be had throughout the tire casing.

As shown in Figs. 'l to 9, inclusive, the conductive layer is formed of a relatively closely spaced meshwork of stretchable metallic conductorsM and 48. .The conductors 41' and 48 may be embedded in conductive rubberlike material'to distribute a potential more evenly over the desired area. Ifthe distance between the metallic conductors is relatively small compared to the thickness of the tire, the conductive rubberlike composition may be eliminated and yet a reasonably effective distribution of potential obtained. By

i varying the spacing of the conductors 4l and 48 and by utilizing a conductive rubberlike composition, it is found, however, that a desired degree of the heating of the composition to just prevent energy dissipation from the vcontact surface of the tire may be obtained. Thus, by increasing the spacing between the conduct/ors or by increasing the resistance of the conductive rubberlike composition, increased conductive heating of the suriace layer i6 may be had, so that it is possible to prevent heat loss from the tire carcass to the air bag. The same effect is also had by supplying heat from an external source to the inner surface Vof thetire, or'by'heating the fluid pressure bag by heating iluid admitted to the cavity defined by the walls thereof.

In accordance with the preferred modication of the present invention, illustrated in Figs. 13 to 16, inclusive, at least one of the two conductive surfaces (the inner conductive surface of the mold or the conductive surface of the air bag) situated on opposite sides of the tire casing is divided into a plurality of separately insulated, annular conductive elements. Means is provided for selectively connecting one or more of said elements to a high frequency source or generator so that formation of heat in one or more selected portions of the tire casing may be had. Thus, the air or fluid pressure bag 2c within the tire casing l may be provided with a plurality of annular conductive elements, such for example as annular conductive elements 60a and 60h, Gla and 5 ib, 62a, and 62h, and 63, and/or the inner surface of the mold may be provided with a plurality of separately insulated annular conductive elements, each with appropriate connecting means for selectively connecting it to a source of electrical energy. y

The conductive elements 60 to 63 preferably comprise Va conductive rubber composition as above set forth and auxiliary metallic conductors 61 ,to 69; inclusive, and 14, althougheitherseparately insulated, spaced, annular, exiblemetalli'crconductors coveringthe desired areas or the conductive rubber composition having suitable means'for makingelectrical contact thereto may beused'alonefto-obtain-a portion-of the benefits of `the present process. The annular conductive elements-50 to S3, which when only a few are used preferably have substantialsurface parallel to the inner surface of the tire, are preferably attached to or'carried byabase v{i6-of suitable stretchable non-conductive -rubberlike material which may serve as the walls of the bag acting as means for retaining the desired fluid pressure within the cavity thereof-and as means for positioning andlinsulating the conductive elements from each other. If, however, the inner conducting surface of 'themold is divided into a plurality of spaced-'separately insulated conductive surfaces orrwires, as setforth above, the fluid pressure bag maybe' 4constructed substantiallyl entirely of con.- ductivevulcanized rubber composition, In either case, since the vtire casing is symmetrical about the longitudinal center line, the annular, separately insulated conductive elements may be disposed and connected in pairs symmetrical about thelongitudinal center lineof the tire.

Thus-in' the fluid pressure bag, the conductors 60a and "50h, which are preferably relatively narrow Iand which are disposed adjacent the shoulder regions'of the tire, may be'connected together in pairs through' a lead lll, which in turn is connected through'the lead 7i and a terminal 'l2 to a terminal 82 of a selector switch which is connectedtothe wire 13 and -which permits'selectiveconnecton to the terminal 25 of the radio frequency generator 5.

The kiiexibleconductors -Gla and Bib are so disposed as-to Ahave substantial areas adjacent the "side wall lportions Vof the. tire `and insulated from the conductors 60 and 62 by annularstrips 'I51and 1B of rubberlikematerial. The conductors Slafand lbmay be connected together vthrough a lead 11 which is connected through a wire i9 and "aterminal 80 to a terminal- Sl'of another separately-operable switch also connected to wire 13.

The annular conductors BZavand 62o disposed inthe air bag so a`sto be adjacent thebead regions ofthe tire' may be connected together through a lead-84 Yto'a wire 85 attached to a terminal t6, which is connected to a terminal 3l of another separately operable switch connected vtofwire 13.

lThe annular Yconductive 'element 63, disposed adjacent the vcrown region of lthe-*tire yand symmetrical'with the longitudinal center line thereof, isc'onnected-through a conductor-88to a terminal 89;whichis-connectedto a terminalllll vof another switch connected to -wire 13.

Although in Fig. 14 for purposes of illustration connecting terminals are ydisposed in relatively close proximityl it is preferred that terminals-l2, 80, 85-and 89, as wellas the `connecting wires "H, 19,85 and `88 be disposed substantial distances from each other so that widely distributed .portions of the tire and ofthe airbag are-subjected toflelds due to energy carried-by the connecting wires themselves.

Leads 10, 1I, 11, 19, 81S, Y88, etc. are preferably of highly flexible material high surface area such as coiled stranded metal disposed within a suitable matrix of non-conductive rubberlike material Toprevent undue curing of diiierent rportions of the tire, the leads "are preferably disposed'as far aspossible from the :conductive surfaces of the mold. Thus,the leads l0,- 1l,'etc. Uare preferably disposed within a tube or Ymatrix 92 of `rubberlike .material and the length of -thelcoiled conductor is'preferably `suiiicient A-to permit-stretching of the-air bag and insertionfin the tire band during expansion i thereof without-tending -to cause separation of connections.

Byprovidingfa layer 93 of non-conductive 'rubberlike material over .the outer surface of the conductive layers v Sia-and SIb in yfthe-sidewall thereof opposite the thinnerportions -of 'the Atire side wall the conductive layer 5I maybe `ofrelatively Agreater width without producing a field f of i too high intensity-and without unduly heatingithe f thinner .portions of -the-tire. AHoweverfby4 increasing the numbery of= separately insulated annular conductive Yelementsv and by=decreasing the width thereof, a relatively even 'cure-maybe had when the entire outer surface of theconductive elements bears-against ther-tire casing.

externally of the `tire leasing, -a substantial 4proportion of rthe benets ofthe present invention may be obtained when conductors are-only dis-- posed opposite .the thicker `regions of the tire. Thus, by the luse of conductors Staand-tub only, so that heat is generated `in situ only n*within-the shoulder portions of the tire, substantial reduction in curing ytime maybe obtained.

To increase the intensity and control ofthe field inthe shouldenportions of -the tirait-is often desirable to.. provide annular conductors having an annular conductive surface 950i relatively small cross sectional extent adjacent the shoulder portions of the tire-and electrically insulated from the conductive surface 2D, which bears against the outer side walls of the -tire by suitable insulation 96, such as` porcelain or other rigid insulating material, which is retained with-A in the mold halves by the shoulder 97 and the removable annular tread-forming annular segments 98.

The conductive surface of the annular separately insulated portion 94 of the mold ispreferably connected through a wire 99 to the center termlna129 of the generator 5 in such a way that.

a separate high frequency potential difference maybe selectively applied between one or more annular elements, such as 60a, of thealr bag and the portion. This is readily permitted by connecting'the mold halvea which makes electrical contactr'with rthe surface 2l) to a grounded terminal 39 of a switch 45,'the other'term'inaldS being connected to the center Yterminal`29 f the high freduencysourceb.

In the curing of tires in accordance with fthe apparatus'illustratedin Figs. nI3 to 16,'inclu'sive, y

the electric field may be specicall'y directed'to Vthe shoulder 'regions by'closing a switch 58 and openingthe switch`45. IAfter a short'treatmena the switch 45 may then be closed and switches 45, 54 and 65 may then be closed in any desired order to lalso subjectthe dielectric material of the next thicker region of the tire to rapid change instrain and thus form heat in situ therein. Since the side wall of the tire is generally relatively thin, it is preferred that switch 51 be closed for a relatively short period of time, and if heat is supplied externally sufcient heating may be had without closing it at all.

It is thus seen that a plurality of annular conductive segments of relatively limited area at one or both surfaces, each segment or each pair of segments having separately insulated connecting means, permits the utilization of any of the desired amount of energy within the respective portions of the tire. Since appreciable amounts of non-conductive insulating material `need not also be disposed in an electric eld, it is seen that greater eiciency of utilization of the high frequency energy is had.

By combining the heat formed in situ with energy applied to one or both external surfaces from steam or heating duid admitted to the catities 6a and 6b, the effects of even slight variations in the electric field may be eliminated.. The extra heat required for the metal of the beads may, as above set forth, he inductively supplied by passing current through the coils 35 having terminals 52 and 53 connected to the transformer 3B that is connected to a suitable source of electrical energy E. If desired. heat may be magnetically or electrically induced within the bead wires as by passing a current of intermediate freouency, say 1000 to 200 000 cycles per second through a coil having windings enclosing only a portion of the two beads (circumventinr the tire cross section) and rotating the beads longitudinally through the coil.

The heat formed throughout a tire of given composition depends, as stated before. on the intensity of the electric field and its rate of change. It is increased hv increasing the potential difference between the opnositely disposed electrodes and by increasing freouencv. The particular freouency used and the particular potential applied may he varied as desired. To obtain the same curing time. in tires of greater cross section. a hierher potential or higher frequency. or both may be used.

Voltarms of the order of one. thousand to twentyve or thirty thousand volts. oreven more are desirable in .tires having relatively thick sections, In tires having relatively thin sections. such as passenger car tires, smaller voltages may be used.

Since the heat is formed in situ throughout the tire in accordance with the present invention` and since the interior portions of the tire may be subiected to the same temperature for the same leneth of time as are the surface regions of the tire, fast or ultra accelerators may be used to cause curing of the tirein but a small fraction of the time required heretofore. In fact, the curing time of heavy duty tiresy having .high cross sectional thickness may be reduced from the two or three hours heretofore required. to as little as one-fourth hour by the selection of faster curing accelerators and by the application of the present invention.

It is to be understood that variations and modifcations of the specific process and apparatus herein shown and described for purposes of illustration may be made without departing from the spirit of the invention.

What I claim is:

jl. A fluid pressure bag for insertion within pneumatic tires during the curing or repairing thereof, comprising a exible stretchable wall portion enclosing a fluid-retaining cavity and fluid conduit means through said wall for passage of infiaton :duid into said cavity, an annular -layer of flexible, electrically conductive material carried by said wall portion, a covering of relatively non-conductive rubberlike composition over at least portions of said layer, the thickness of said covering being greater at the portions of said bag adapted to bear against the side wall of said casing than at the portions adapted to bear against the shoulder portions thereof, and leads extending from said layer to the exterior of said bag for connecting -said layer to a suitable source of high frequency electrical energy.

2. Apparatus for repairing or curing pneumatic tire casings comprising a mold to receive said tire casing and having an inner rigid forming surface adapted to bear against the exterior of said casing, a fluid pressure bag adapted to be disposed inside of said casing and having an outer surface adapted to bear against the inner surface of said casing to press said casing strongly against said rigid forming surface of said mold, said air bag having a flexible, stretchable wall portion thereof enclosing a fluid-retaining cavity, a flexible, annular, conductive element vcarried hy said wall portion, means for applying heating fluid to said mold to conductively heat said forming surface thereof, means for supplying heating fluid to said fluid-retaining cavity, and means for applying a high frequency electrical potential difference between only an annular portion of said forming surface and said annular conductive element, said annular portion of-said forming surface having an area less than the area of said forming surface, whereby an electri cal potential difference may be applied between said air bag and said mold to subject portions only of said tire casing to a high frequency electric field.

3. Apparatus for repairing or curing pneumatic tire casings comprising a mold to receive said tire casing andV having an inner rigid forming surface adapted to bear against the exterior of said casing, a fiuid pressure bag adapted to be disposed inside of said casing and having anv outer surface adapted to bear against the inner surface of said casing to press said casing strongly against said rigid forming surface of said mold, said air bag having a flexible, stretchable wall portion thereof enclosing a fluid-retaining cavity, a fiexible, annular, conductive element carried by said wall portion, means for applying heating fluid to said mold to conductively heat said forming surface thereof, means for supplying heating fluid to said fluid-retaining cavity, said mold having in the region of the forming surface thereof a plurality of separately insulated, annular, electrically conductive elements, and means for making electrical connections to said elements, whereby an electrical potential dierence may be applied between said air bag and said mold to subject portions only of said tire casing to a high frequency electric field.

4. Apparatus for repairing or curing pneumatic tire casings comprising a mold to receive said tire casing and having an inner rigid forming surface adapted to bear against the exterior of said casing, a fluid pressure bag adapted to be disposed inside of said casing and having an outer surface adapted to bear against the inner surface of said casing to press said casing strongly against said rigid forming surface of said mold, said air bag having a exible, stretchable wall said wall portion, means for applying heating iluid to said mold to conductively heat said forming surface thereof, means for supplying heating uid to said iiuid-retaining cavity, means for applying a high frequency electrical potential difference between only an annular portion of said forming surface and said annular conductive element, which annular portion has less area than the area of said forming surface, and means for inductively heating the metal of said beads, whereby an electrical potential dierence may be applied between said air bag and said mold to subject portions only of said tire casing to a high frequency electric eld.

5. Apparatus for curing or repairing pneumatic tire casings comprising a mold to receive the tire casing and having a rigid forming surface adapted to extend over the external surface of said tire casing, means for supplying heating fluid to heat said forming surface, a fluid pressure bag, with an annular uid-retaining cavity enclosed by a flexible stretchable Wall, having a forming surface adapted to bear against the internal surf-ace of said tire casing when it is disposed therein, said iiuid pressure bag having at least one annular conductive element to be disposed inside said tire casing and the mold having at least one conductive element adapted to be disposed outside said tire casing, the total number of conductive elements in said mold and in said bag being numerically more than two to provide a plurality of annular conductive elements on one side of said tire placed in said mold with said fluid pressure bag therein and at least one conductive element on the other side of said tire, said plurality of annular conductive elements on one side of said tire being laterally spaced from each other by insulating material, and means for separately connecting at least some of said elements to a high frequency potential whereby a potential difference may be selectively applied between portions of said conductive elements on opposite sides of said tire casing to selectively subject annular portions only of said tire casing to high frequency electrical stress.

THEODORE A. TE GROIENHUIS.

REFERENCES CITED The following references are of record ln the le of this patent:

UNITED STATES PATENTS Number Name Date 1,216,654 Burke Feb. 20, 1917 1,923,736 Lewis et al. Aug. 22, 1933 1,924,530 Woock Aug. 29, 1933 2,324,644 Powell et a1 July 20, 1943 2,342,846 Crandell Feb. 29, 1944 2,370,624 Gillespie Mar. 6, 1945 2,280,771 Dufour et a1 Apr. 28, 1942 

